This invention relates to the field of solid state electronics and particularly to field-effect transistors (FETs).
Metal-semiconductor field-effect transistors (MESFETs) fabricated on semi-insulating substrates such as GaAs usually suffer from the so-called "substrate effect", normally considered responsible for undesirable device behavior such as looping in the drain current-voltage characteristics and sensitivity to light. The origin of this effect is the existence of a space-charge region, caused by deep-level impurity traps in the substrate, at the interface between the n-type channel (or active) layer and the substrate. This effect is usually reduced if an additional GaAs buffer layer is grown between the substrate and the channel layer so that the traps in the substrate are not "seen" by the channel layer. This method, however, requires an extra epitaxial growth procedure and is not compatible with the all-implantation fabrication approach.